Device and method for control of flexible link robot manipulators

• US 5,049,797 A
• Filed: 07/02/1990
• Issued: 09/17/1991
• Est. Priority Date: 07/02/1990
• Status: Expired due to Fees

• Current Assignee: Utah State University Foundation A Non-Profit Organization of Utah
• Original Assignee: Utah Valley University
• Inventors: Phillips, Warren F.
• Primary Examiner(s): Ip, Paul
• Application Number:
  US07/546,924
• Time in Patent Office: 442 Days
• Field of Search: 318/560-646, 364/513, 901/3, 901/6, 901/9, 901/12-23, 901/46, 901/47, 901/48, 414/730, 414/731, 414/732, 414/735, 356/152
• US Class Current: 318/568.16
• CPC Class Codes: B25J 9/1635 flexible-arm control

Abstract

A method and device for controlling and dampening undesirable vibrational movement within flexible linkage of a robot arm coupled to a movable, controlled joint and attached drive motor. The method includes the steps of providing position displacement and control in accordance with position and velocity feedback input. In addition, elastic deflection arising within the robot arm is detected and a time-dependent deflection signal proportional to the degree of elastic deflection is generated. A control algorithm develops deflection feedback signals for input to the robot arm which are approximately proportional to the deflection signal and its first two time derivatives, each multiplied by a gain whose value is selected to reduce further elastic deflection. This procedure is applied within flexible robot arm structure by incorporating elastic deflection detection components and by converting the detected deflection signal to deflection feedback signals for application to the drive system of the robot arm. Elastic deflections arising upon movement of the flexible arm structure are almost immediately nullified and the robot arm is allowed to reposition itself without interference from such undesirable forces and resultant robot arm movement.

Claims

1. A method for controlling and dampening undesirable, vibrational movement within flexible linkage of a robot arm coupled to a moveable, controlled joint and attached drive motor, said method comprising the steps of:

1.1 determining a position displacement required to move the robot arm from the current position to a desired position;

1.2 activating the drive motor to reposition the robot arm to the desired position;

1.3 generating a position feedback signal to enable adjustment of the changing positions of the robot arm to efficiently move the arm toward the desired position;

1.4 detecting any elastic deflection arising within the robot arm;

1.5 generating a time dependent deflection signal proportional to a degree of elastic deflection of step 1.4;

1.6 generating a deflection feedback signal for input to the robot arm wherein the deflection feedback signal is approximately proportional to the deflection signal, multiplied by a gain whose value is selected to reduce further elastic deflection of the robot arm;

1.7 applying the deflection feedback signal to the robot arm to reduce further elastic deflection; and

1.8 continuously performing the procedures of steps 1.3 through 1.7 until the robot arm is properly located in the desired position.

2. A method as defined in claim 1, further comprising the more specific steps of:

2.1 generating a continuous analog deflection signal proportional to the degree of elastic deflection;

2.2 continuously generating a deflection feedback signal for input to the robot arm by multiplying the analog deflection signal by a gain whose value is selected to reduce further elastic deflection of the robot arm;

2.3 applying the analog deflection signal to the robot arm to reduce further elastic deflection within the robot arm.

3. A method as defined in claim 2, wherein step 2,3 of applying the deflection feedback signal to the robot arm comprises the more specific steps of feeding the deflection feedback signal to the drive motor in instantaneous manner to impose a counter force in the robot arm which approximates the magnitude of deflection force being applied to cause the elastic deflection but in opposing direction to at least partially nullify further elastic deflection arising from such deflection force.

4. A method as defined in claim 1, further comprising the more specific steps of:

4.1 generating a time dependent digital deflection signal proportional to the degree of elastic deflection;

4.2 generating a deflection feedback signal for input to the robot arm by multiplying the digital deflection signal by a gain whose value is selected to reduce further elastic deflection of the robot arm;

4.3 applying the digital deflection signal to the robot arm to reduce further elastic deflection within the robot arm; and

4.4 continuously repeating the procedures of 4.1 through 4.3 until the robot arm is properly located in the desired position.

5. A method as defined in claim 1, wherein step 1.7 of applying the deflection feedback signal to the robot arm comprises the more specific steps of feeding the deflection feedback signal to the drive motor in instantaneous manner to impose a counter force in the robot arm which approximates the magnitude of deflection force being applied to cause the elastic deflection but in opposing direction to at least partially nullify further elastic deflection arising from such deflection force.

6. A method as defined in claim 1, wherein the step of detecting deflection within the robot arm comprises the more specific steps of:

6.1 optically monitoring the relative positions of the flexible link with respect to the controlled joint; and

6.2 detecting the degree of elastic displacement of the flexible link out of the relative position corresponding to the degree of elastic deflection.

7. A method as defined in claim 1, wherein the step of detecting deflection within the robot arm comprises the more specific steps of:

7.1 applying strain gages along a flexible length of the robot arm; and

7.2 generating a deflection signal from each of the strain gages which is proportional to the degree of elastic deflection of flexible link.

8. A method as defined in claim 1, further comprising the steps of:

8.1 determining a first time derivative of the deflection detected in step 1.4 corresponding to the velocity of the elastic deflection,

8.2 multiplying the first derivative by a first desired gain, and

8.3 combining the product of 8.2 with the deflection feedback signal of step 1.6 to more efficiently reduce further dynamic elastic deflection while countering the affect of static elastic deflection.

9. A method as defined in claim 8, further comprising the steps of:

9.1 determining a second time derivative of the deflection detected in step 1.4 corresponding to the acceleration of the elastic deflection,

9.2 multiplying the second derivative by a second desired gain, and

9.3 combining the product of 9.2 with the deflection feedback signal of step 1.6 to more efficiently reduce further dynamic elastic deflection while countering the effect of static elastic deflection.

10. A method as defined in claim 1, wherein the position feedback signals and deflection feedback signals comprise voltages to be supplied to the drive motor which values are proportional to the amount of deflection to be applied to the robot arm, said method comprising the specific steps of:

10.1 generating a deflection feedback signal voltage corresponding to an amplitude of the deflection signal of step 1.5;

10.2 reversing polarity of the deflection feedback signal voltage; and

10.3 applying the voltage of step 10.2 to the drive motor.

11. A method as defined in claim 10, further comprising the steps of:

11.1 generating a voltage signal proportional to a first time derivative of the deflection feedback signal of step 10.1, and

11.2 combining the first time derivative voltage with the voltage of the deflection feedback signal; and

11.3 applying this voltage to the drive motor to dampen elastic deflection within the robot arm.

12. A method as defined in claim 11, further comprising the steps of:

12.1 generating a voltage signal proportional to a second time derivative of the deflection feedback signal of step 10.1, and

14. A method as defined in claim 1, further comprising the step of generating a velocity feedback signal in conjunction with the position feedback signal for enabling more effective adjustment of the changing positions and rate of change for the robot arm.

17. A device as defined in claim 14, wherein the robot arm operates in a planar movement path, said detecting means being operable to detect elastic deflection with respect to movement within a plane of robot arm movement.

18. A device as defined in claim 14, wherein the robot arm operates in a multiplanar movement path, said detecting means being operable to detect elastic deflection with respect to three-dimensional movement of the robot arm.

19. A device as defined in claim 14, wherein the robot arm further comprises a plurality of flexible links, each link including a detecting means for detecting elastic deflection within that link and corresponding deflection signal generating means and deflection feedback means as set forth in paragraphs 14.4 and 14.5.

13. 2 combining the second time derivative voltage with the voltage of the deflection feedback signal;

and

12.3 applying the to the drive motor to dampen elastic deflection within the robot arm.

15. A device for controlling and dampening undesirable vibrational movement within flexible linkage of a robot arm coupled to a moveable, controlled joint and attached drive motor, said device comprising:

14.1 computing means for determining the position displacement required to move the robot arm from the current position to a desired position;

14.2 a drive motor coupled to the robot arm and the computer means to reposition the robot arm to the desired position;

14.3 position feedback means in connection with the computer means for generating a position feedback signal to enable adjustment by the computer means of the changing positions of the robot arm to efficiently move the arm toward the desired position;

14.4 detecting means coupled to the robot arm for detecting any elastic deflection arising within the robot arm;

16. 5 deflection signal generating means coupled to the detecting means and computer means for generating a deflection signal dependent in value upon the degree of elastic deflection experienced within the robot arm;

14.6 deflection feedback means in connection with the computer means for generating a deflection feedback signal for input to the robot arm which is proportional to the deflection signal, multiplied by a gain which value is selected to reduce further elastic deflection within the robot arm; and

14.7 counter displacement means for applying the deflection feedback signal to the robot arm to reduce further deflection.